Optical imaging system

ABSTRACT

An optical imaging system includes a first lens group that can move in an optical direction and has negative refractive power; a second lens group that can move in the optical direction and has positive refractive power; and a third lens group that can move in the optical direction and has negative refractive power. The first lens group, the second lens group, and the third lens group include seven lenses in total, and at least one of the seven lenses includes an aspherical surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(a) of Korean PatentApplication No. 10-2018-0044964 filed on Apr. 18, 2018 and Korean PatentApplication No. 10-2018-0115988 filed on Sep. 28, 2018 in the KoreanIntellectual Property Office, the entire disclosures of which areincorporated herein by reference for all purposes.

BACKGROUND 1. Field

The following description relates to an optical imaging system capableof adjusting a focal length.

2. Description of Background

A collapsible optical imaging system in which a plurality of lenses isaligned in a row is configured such that the greater the number oflenses, the longer the overall length of the optical imaging system. Forexample, it may be more difficult to reduce a size of an optical imagingsystem including five lenses further than an optical imaging systemincluding three lenses. For this reason, there may be a limitation inmounting a collapsible optical imaging system in a small-sized portableterminal device.

Differently from a collapsible optical imaging system, a curved opticalimaging system may be configured such that an optical direction iscurved using a prism, and a length from a foremost lens to an imagingplane may accordingly be reduced. However, the amount of displacement ofa lens group to adjust a focus may be large in the curved opticalimaging system, and thus, it may be difficult to reduce a size of thecurved optical imaging system.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, an optical imaging system includes a first lensgroup that can move in an optical direction and has negative refractivepower; a second lens group that can move in the optical direction andhas positive refractive power; and a third lens group that can move inthe optical direction and has negative refractive power. The first lensgroup, the second lens group, and the third lens group include sevenlenses in total, and at least one of the seven lenses includes anaspherical surface.

At least one of the seven lenses may be made of a plastic material.

The first lens group may include two lenses having refractive power withdifferent signs.

The second lens group may include three lenses, and the three lenses ofthe second lens group may be disposed such that the three lenses haverefractive power having signs different from signs of refractive powerof adjacent lenses in the second lens group.

The third lens group may include two lenses having refractive power withdifferent signs.

The optical imaging system may include a refractive prism disposed infront of the first lens group.

In another general aspect, an optical imaging system includes a prism; afirst lens having positive refractive power; a second lens havingnegative refractive power; a third lens having positive refractivepower; a fourth lens having negative refractive power; a fifth lenshaving positive refractive power; a sixth lens having positiverefractive power; and a seventh lens having negative refractive power.The prism and the first to seventh lenses are sequentially disposed froman object side.

The first lens may include a convex image-side surface.

The second lens may include a convex object-side surface.

The third lens may include a convex image-side surface.

The fourth lens may include a concave object-side surface.

The sixth lens may include a concave object-side surface.

The seventh lens may include a concave image-side surface.

The optical imaging system may satisfy −1.0<(R1+R2)/(R1−R2)<−0.1, whereR1 is a radius of curvature of an object-side surface of the first lens,and R2 is a radius of curvature of an image-side surface of the firstlens.

The optical imaging system may satisfy 0.11<Nd6−Nd7<0.13, where Nd6 is arefractive index of the sixth lens, and Nd7 is a refractive index of theseventh lens.

At a wide-angle end of the optical imaging system, a distance D1 betweenthe first lens group and the second lens group may be greater than adistance D3 between the third lens group and an imaging plane, and adistance D2 between the second lens group and the third lens group maybe greater than D3.

D1/D2 may be within a range of 0.9 to 1.3, D2/D3 may be within a rangeof 1.5 to 2.2, and D1/D3 may be within a range of 1.5 to 3.5.

At a telephoto end of the optical imaging system, a distance D1 betweenthe first lens group and the second lens group may be smaller than adistance D2 between the second lens group and the third lens group, andD2 may be smaller than a distance D3 between the third lens group and animaging plane.

D1/D2 may be within a range of 0.2 to 0.4, D2/D3 may be within a rangeof 0.2 to 0.4, and D3/D1 may be within a range of 14 to 16.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a first example of an optical imagingsystem.

FIG. 2 illustrates aberration curves in a first variable magnificationposition of the optical imaging system illustrated in FIG. 1.

FIG. 3 illustrates aberration curves in a second variable magnificationposition of the optical imaging system illustrated in FIG. 1.

FIG. 4 is a diagram illustrating a second example of an optical imagingsystem.

FIG. 5 illustrates aberration curves in a first variable magnificationposition of the optical imaging system illustrated in FIG. 4.

FIG. 6 illustrates aberration curves in a second variable magnificationposition of the optical imaging system illustrated in FIG. 4.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent after an understanding of thedisclosure of this application. For example, the sequences of operationsdescribed herein are merely examples, and are not limited to those setforth herein, but may be changed as will be apparent after anunderstanding of the disclosure of this application, with the exceptionof operations necessarily occurring in a certain order. Also,descriptions of features that are known in the art may be omitted forincreased clarity and conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided merelyto illustrate some of the many possible ways of implementing themethods, apparatuses, and/or systems described herein that will beapparent after an understanding of the disclosure of this application.

Herein, it is noted that use of the term “may” with respect to anexample or embodiment, e.g., as to what an example or embodiment mayinclude or implement, means that at least one example or embodimentexists in which such a feature is included or implemented while allexamples and embodiments are not limited thereto.

Throughout the specification, when an element, such as a layer, region,or substrate, is described as being “on,” “connected to,” or “coupledto” another element, it may be directly “on,” “connected to,” or“coupled to” the other element, or there may be one or more otherelements intervening therebetween. In contrast, when an element isdescribed as being “directly on,” “directly connected to,” or “directlycoupled to” another element, there can be no other elements interveningtherebetween.

As used herein, the term “and/or” includes any one and any combinationof any two or more of the associated listed items.

Although terms such as “first,” “second,” and “third” may be used hereinto describe various members, components, regions, layers, or sections,these members, components, regions, layers, or sections are not to belimited by these terms. Rather, these terms are only used to distinguishone member, component, region, layer, or section from another member,component, region, layer, or section. Thus, a first member, component,region, layer, or section referred to in examples described herein mayalso be referred to as a second member, component, region, layer, orsection without departing from the teachings of the examples.

Spatially relative terms such as “above,” “upper,” “below,” and “lower”may be used herein for ease of description to describe one element'srelationship to another element as shown in the figures. Such spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,an element described as being “above” or “upper” relative to anotherelement will then be “below” or “lower” relative to the other element.Thus, the term “above” encompasses both the above and below orientationsdepending on the spatial orientation of the device. The device may alsobe oriented in other ways (for example, rotated 90 degrees or at otherorientations), and the spatially relative terms used herein are to beinterpreted accordingly.

The terminology used herein is for describing various examples only, andis not to be used to limit the disclosure. The articles “a,” “an,” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. The terms “comprises,” “includes,”and “has” specify the presence of stated features, numbers, operations,members, elements, and/or combinations thereof, but do not preclude thepresence or addition of one or more other features, numbers, operations,members, elements, and/or combinations thereof.

Due to manufacturing techniques and/or tolerances, variations of theshapes shown in the drawings may occur. Thus, the examples describedherein are not limited to the specific shapes shown in the drawings, butinclude changes in shape that occur during manufacturing.

The features of the examples described herein may be combined in variousways as will be apparent after an understanding of the disclosure ofthis application. Further, although the examples described herein have avariety of configurations, other configurations are possible as will beapparent after an understanding of the disclosure of this application.

Hereinafter, examples will be described with reference to the attacheddrawings.

A first lens may refer to a lens disposed most adjacent to an object (ora subject), and a fifth lens may refer to a lens disposed most adjacentto an imaging plane (or an image sensor). In the examples, an entiretyof a radius of curvature, a thickness, a TTL, an IMG HT (½ of andiagonal length of the imaging plane), and a focal length of a lens areindicated in millimeters (mm). Also, a thickness of a lens, a gapbetween lenses, and the TTL may be distances at an optical axis of alens. In a description of a form of a lens, a surface of a lens beingconvex indicates that an optical axis region of the surface is convex,while a surface of a lens being concave indicates that an optical axisregion of the surface is concave. Therefore, in a configuration in whicha surface of a lens is described as being convex, an edge region of thelens may be concave. In a similar manner, in a configuration in which asurface of a lens is described as being concave, an edge region of thelens may be convex.

The optical imaging system may include an optical system including aplurality of lenses. For example, the optical system of the opticalimaging system may include a plurality of lenses having refractivepower. However, the optical imaging system does not only include thelenses having refractive power. For example, the optical imaging systemmay include a prism refracting incident light, and a stop for adjustingthe amount of light. The optical imaging system may further include aninfrared light blocking filter for blocking infrared light. The opticalimaging system may further include an image sensor (an imaging device)for converting an image of a subject incident through the optical systeminto an electrical signal. The optical imaging system may furtherinclude a gap maintaining member for adjusting a distance betweenlenses.

The plurality of lenses may be made of a material having a refractiveindex different from a refractive index of air. For example, theplurality of lenses may be made of a glass material. At least one of theplurality of lenses may be aspherical. The aspherical surface may berepresented by Equation 1 below.

$\begin{matrix}{Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {Ar}^{4} + {Br}^{6} + {Cr}^{8} + {Dr}^{10} + {Er}^{12} + {Fr}^{14} + {Gr}^{16} + {Hr}^{18} + {Jr}^{20}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

In Equation 1, “c” is an inverse of a radius of a curvature of arespective lens, “K” is a conic constant, “r” is a distance from acertain point on an aspherical surface of the lens to an optical axis,“A” to “J” are aspheric constants, “Z” (or SAG) is a height from acertain point on an aspherical surface of the lens to an apex of theaspherical surface in an optical axis direction.

The optical imaging system may include a plurality of lens groups. Forexample, the optical imaging system may include a first lens group, asecond lens group, and a third lens group. The first lens group, thesecond lens group, and the third lens group may be disposed in orderalong an optical axis.

The first lens group may include a plurality of lenses. For example, thefirst lens group may include a plurality of lenses having refractivepower with different signs. For example, the first lens group mayinclude a lens having positive refractive power and a lens havingnegative refractive power. Overall, lenses of the first lens group mayhave negative refractive power.

The second lens group may include a plurality of lenses. For example,the second lens group may include three lenses. The three lenses of thesecond lens group may be disposed such that one lens among the threelens may have refractive power having different signs from signs ofrefractive power of adjacent lenses. For example, the second lens groupmay include a lens having positive refractive power, a lens havingnegative refractive power, and a lens having positive refractive power.Overall, lenses of the second lens group may have positive refractivepower.

The third lens group may include a plurality of lenses. For example, thethird lens group may include a plurality of lenses having refractivepower with different signs. For example, the third lens group mayinclude a lens having positive refractive power and a lens havingnegative refractive power. Overall, lenses of the third lens group mayhave negative refractive power.

The first to third lens groups may move in an optical direction. Forexample, at least one or more of the first to third lens groups may moveto change a focal length of the optical imaging system, and two or moreof the first to third lens groups may move to adjust a focus of theoptical imaging system. Thus, the optical imaging system maysignificantly change a variable magnification ratio. Further, in theoptical imaging system, the plurality of lens groups may be driven toadjust a focus, and thus, a precise focus adjustment may be available inany variable magnification conditions, and a range of displacement ofthe lens groups to adjust a focus may be significantly reduced.

The optical imaging system may include a lens made of a plasticmaterial. For example, the optical imaging system may be configured suchthat one of seven or more lenses included in the lens groups may be madeof a plastic material.

The optical imaging system may include an aspherical lens. For example,the optical imaging system may be configured such that one of seven ormore lenses included in the lens groups may be an aspherical lens.

The optical imaging system may include a prism, a filter, a stop, and animage sensor.

The prism may be disposed in an object side of the first lens group. Theprism may include a material having a relatively low Abbe number. Forexample, a material of the prism may be selected from materials havingan Abbe number of 25 or lower.

The filter may be disposed between the third lens group and the imagesensor. The filter may block a certain wavelength of incident light toimprove a resolution of the optical imaging system. For example, thefilter may block infrared wavelengths of incident light.

The stop may be disposed between the first lens group and the secondlens group.

The optical imaging system may satisfy one or more of the followingfirst to seventh conditional expressions:

−1.5<R2/f<−0.5  (Conditional Expression 1)

−1.0<(R1+R2)/(R1-R2)<−0.1  (Conditional Expression 2)

0.1<f/f1<0.8  (Conditional Expression 3)

1.0<f/f3<3.0  (Conditional Expression 4)

−1.5<f/f4<−0.2  (Conditional Expression 5)

0.2<f/f5<1.0  (Conditional Expression 6)

0.11<N6−N7<0.13  (Conditional Expression 7)

In the conditional expressions, “f” is a focal length of the opticalimaging system, R1 is a radius of curvature of an object-side surface ofthe first lens, R2 is a radius of curvature of an image-side surface ofthe first lens, f1 is a focal length of the first lens, f3 is a focallength of the third lens, f4 is a focal length of the fourth lens, f5 isa focal length of the fifth lens, N6 is a refractive index of the sixthlens, and N7 is a refractive index of the seventh lens.

In the following description, various examples of the optical imagingsystem will be described.

A first example of the optical imaging system will be described withreference to FIG. 1.

The optical imaging system 100 may include a prism 102, a first lens110, a second lens 120, a third lens 130, a fourth lens 140, a fifthlens 150, a sixth lens 160, and a seventh lens 170, and may be dividedinto a plurality of lens groups. For example, the optical imaging system100 may be divided into a first lens group G1, a second lens group G2,and a third lens group G3. The first lens group G1 may include twolenses. For example, the first lens group G1 may include the first lens110 and the second lens 120. The first lens 110 may have positiverefractive power, and may have a convex object-side surface and a conveximage-side surface. The second lens 120 may have negative refractivepower, and may have a convex object-side surface and a concaveimage-side surface. The second lens group G2 may include three lenses.For example, the second lens group G2 may include the third lens 130,the fourth lens 140, and the fifth lens 150. The third lens 130 may havepositive refractive power, and may have a convex object-side surface anda convex image-side surface. The fourth lens 140 may have negativerefractive power, and may have a concave object-side surface and aconvex image-side surface. The fifth lens 150 may have positiverefractive power, and may have a concave object-side surface and aconvex image-side surface. The third lens group G3 may include twolenses. For example, the third lens group G3 may include the sixth lens160 and the seventh lens 170. The sixth lens 160 may have positiverefractive power, and may have a concave object-side surface and aconvex image-side surface. The seventh lens 170 may have negativerefractive power, and may have a convex object-side surface and aconcave image-side surface.

The lens groups G1, G2, and G3 may move in an optical direction tochange a focal length of the optical imaging system. For example, adistance D1 between the first lens group G1 and the second lens group G2and a distance D2 between the second lens group G2 and the third lensgroup G3 may be reduced as a focal length of the optical imaging systemis lengthened. Also, a distance D3 between the third lens group G3 andthe imaging plane may be increased as a focal length of the opticalimaging system is lengthened.

The lens groups G1, G2, and G3 may move in an optical direction toswiftly adjust a focus of the optical imaging system. For example, atleast one or more of the first lens group G1, the second lens group G2,and the third lens group G3 may move in an optical direction such that aclear image of a subject may be imaged on the imaging plane. Further,the first lens group G1, the second lens group G2, and the third lensgroup G3 may move by different distances in an optical direction tosignificantly reduce the amount of displacement for focal adjustment.The optical imaging system 100 may have aberration characteristicsillustrated in FIGS. 2 and 3.

The optical imaging system 100 may include the prism 102, a stop ST, afilter 180, and an image sensor 190.

The prism 102 may be disposed in front of the first lens 110. The prism102 may refract light reflected from an object side to the first lens110.

The filter 180 may be disposed in front of the image sensor 190, and mayblock infrared light, and the like, included in incident light. Theimage sensor 190 may include a plurality of optical sensors. The imagesensor 190 may be configured to convert an optical signal into anelectrical signal.

Table 1 lists characteristics of the lenses of the optical imagingsystem 100, Table 2 lists aspheric values of the optical imaging system100, and Table 3 lists distance values between the lens groups in afirst position and a second position of the optical imaging system 100.

TABLE 1 f = 6.0~9.0 First Example F No. = 2.2~3.0 Surface Radius ofThickness/ EFL (e- Abber No. Note Curvature Distance line) index No. objinfinity infinity  1 Prism infinity 2.320 1.6349 23.9  2 infinity 2.3201.6349 23.9  3 infinity 0.700  4* First lens 22.0000 0.800 22.381 1.634923.9  5* −40.7794 0.250  6* Second 5.2882 0.800 −7.426 1.5441 56  7*lens 2.1735 0.400  8 Stop infinity D1  9* Third lens 2.4358 1.000 3.231.5441 56 10* −5.4819 0.300 11* Fourth −2.6572 0.550 −9.592 1.66 20.412* lens −4.9126 0.346 13* Fifth lens −137.6539 0.506 10.663 1.5441 5614* −5.5984 D2 15* Sixth lens −3.8212 1.480 42.59 1.66 20.4 16* −3.89200.366 17* Seventh 11.0643 0.500 −5.813 1.5441 56 18* lens 2.4288 D3 19Filter infinity 0.210 1.5167 64.1 20 infinity 0.340 21 Imaging infinity0.002 Plane

TABLE 2 Surface No. K A B C D E F G 4 35.0588481 0.00605825 −0.00113020.00027913 −8.82E−05 2.07E−05 3.31E−07 −2.55E−07 5 0 0.02118025−0.0082438 0.0017682 −0.000318 9.99E−05 −1.75E−05 2.25E−06 6 0−0.0054839 −0.0087683 0.00119182 0.00010743 7 0 −0.042412 −0.0015924 9 0−0.0054625 −0.0002251 0.0001103 0.00025993 −1.46E−04 3.07E−05 −2.63E−0710 0 0.00888872 0.00504013 −0.0007601 0.00012551 −2.85E−04 5.83E−051.34E−07 11 0 0.05573568 0.00013543 −0.0021669 −0.0002342 12 00.03494754 0.00191593 −0.0014391 −0.000219 13 0 −0.0186447 −0.00017010.00112704 0.00137094 −4.31E−04 5.76E−06 −2.78E−07 14 0 3.86E−04−9.08E−03 4.85E−03 1.50E−04 −2.88E−04 4.21E−05 −2.27E−07 15 0 3.42E−02−1.76E−02 5.28E−03 −2.87E−04 −2.32E−04 2.00E−07 −1.20E−13 16 0 3.27E−02−1.73E−02 5.48E−03 2.20E−04 −3.67E−04 4.18E−05 2.27E−08 17 0 −1.02E−011.52E−02 4.09E−03 −1.55E−03 1.44E−04 18 0 −1.44E−01 4.79E−02 −1.16E−021.54E−03 −8.97E−05

TABLE 3 1st 2nd Position Position D1 1.6775 0.2 D2 1.3325 0.6 D3 0.8 3

A second example of the optical imaging system will be described withreference to FIG. 4.

The optical imaging system 200 may include a prism 202, a first lens210, a second lens 220, a third lens 230, a fourth lens 240, a fifthlens 250, a sixth lens 260, and a seventh lens 270, and may be dividedinto a plurality of lens groups. For example, the optical imaging system200 may be divided into a first lens group G1, a second lens group G2,and a third lens group G3. The first lens group G1 may include twolenses. For example, the first lens group G1 may include the first lens210 and the second lens 220. The first lens 210 may have positiverefractive power, and may have a convex object-side surface and a conveximage-side surface. The second lens 220 may have negative refractivepower, and may have a convex object-side surface and a concaveimage-side surface. The second lens group G2 may include three lenses.For example, the second lens group G2 may include the third lens 230,the fourth lens 240, and the fifth lens 250. The third lens 230 may havepositive refractive power, and may have a convex object-side surface anda convex image-side surface. The fourth lens 240 may have negativerefractive power, and may have a concave object-side surface and aconvex image-side surface. The fifth lens 250 may have positiverefractive power, and may have a convex object-side surface and a conveximage-side surface. The third lens group G3 may include two lenses. Forexample, the third lens group G3 may include the sixth lens 260 and theseventh lens 270. The sixth lens 260 may have positive refractive power,and may have a concave object-side surface and a convex image-sidesurface. The seventh lens 270 may have negative refractive power, andmay have a convex object-side surface and a concave image-side surface.

The lens groups G1, G2, and G3 may move in an optical direction tochange a focal length of the optical imaging system. For example, adistance D1 between the first lens group G1 and the second lens group G2and a distance D2 between the second lens group G2 and the third lensgroup G3 may be reduced as a focal length of the optical imaging systemis lengthened. Also, a distance D3 between the third lens group G3 andthe imaging plane may be increased as a focal length of the opticalimaging system is lengthened.

The lens groups G1, G2, and G3 may move in an optical direction toswiftly adjust a focus of the optical imaging system. For example, atleast one or more of the first lens group G1, the second lens group G2,and the third lens group G3 may move in an optical direction such that aclear image of a subject may be imaged on the imaging plane. Further,the first lens group G1, the second lens group G2, and the third lensgroup G3 may move by different distances in an optical direction tosignificantly reduce the amount of displacement for focal adjustment.The optical imaging system 200 may have aberration characteristicsillustrated in FIGS. 5 and 6.

The optical imaging system 200 may include the prism 202, a stop ST, afilter 280, and an image sensor 290.

The prism 202 may be disposed in front of the first lens 210. The prism202 may refract light reflected from an object side to the first lens210.

The filter 280 may be disposed in front of the image sensor 290, and mayblock infrared light, and the like, included in incident light. Theimage sensor 290 may include a plurality of optical sensors. The imagesensor 290 may be configured to convert an optical signal into anelectrical signal.

Table 4 lists characteristics of the lenses of the optical imagingsystem 200, Table 5 lists aspheric values of the optical imaging system200, and Table 6 lists distance values between the lens groups in afirst position and a second position of the optical imaging system 200.

TABLE 4 f = 6.0~9.0 Second Example F No. = 2.2~3.0 Surface Radius ofThickness/ EFL (e- Abber No. Note Curvature Distance line) index No. objinfinity infinity  1 Prism infinity 2.32 1.6349 23.9  2 infinity 2.321.6349 23.9  3 infinity 0.7  4* First lens 800.25 0.8312 28.430 1.634923.9  5* −18.64867 0.2500  6* Second 4.110698 0.8000 −7.719 1.5311 55.7 7* lens 1.91775 0.3725  8 Stop infinity D1  9* Third lens 2.402811.0000 3.286 1.5311 55.7 10* −5.54501 0.1958 11* Fourth −3.570563 0.7043−9.520 1.66 20.4 12* lens −8.791745 0.1200 13* Fifth lens 15.548710.5283 11.699 1.5311 55.7 14* −10.30075 D2 15* Sixth lens −3.9537671.2805 31.939 1.66 20.4 16* −3.767758 0.4127 17* Seventh 11.06313 0.5000−5.998 1.5311 55.7 18* lens 2.442708 D3 19 Filter infinity 0.21 1.516764.1 20 infinity 0.339993 21 Imaging infinity −0.005876 Plane

TABLE 5 Surface No. K A B C D E F G 4 −99 0.01187846 −0.00267430.00093406 −1.16E−04 −2.38E−06 3.28E−06 −2.56E−07 5 0 0.01351841−0.0049422 0.00264485 −0.0005382 3.00E−05 5.95E−06 7.55E−07 6 0−0.0436161 8.15E−05 0.00370749 −0.0015824 2.61E−04 −2.84E−06 −1.89E−06 70 −0.0830232 0.01136849 −0.0042653 0.00081745 −1.63E−04 9.84E−07−1.55E−12 9 0 −0.0067639 −0.000987 0.00037564 0.00013021 −1.54E−045.26E−05 −2.63E−07 10 0 0.00475946 0.00525361 0.00061199 −0.000287−2.27E−04 5.83E−05 1.34E−07 11 0 0.02690547 0.00438778 0.00097024−0.0017541 2.47E−04 −2.91E−05 2.14E−07 12 −7.9787316 0.016215410.00307348 0.00242223 −0.0011522 −5.23E−04 1.53E−04 −8.72E−09 13 0−0.0124493 −0.0021431 0.00231014 −0.0003794 −7.53E−06 5.76E−06 −2.78E−0714 0 3.52E−05 −8.21E−03 8.19E−04 1.07E−03 −2.70E−04 4.21E−05 −2.27E−0715 0 2.98E−02 −1.89E−02 5.13E−03 −2.64E−04 −2.32E−04 2.00E−07 −1.16E−1316 0 3.58E−02 −2.03E−02 7.55E−03 −7.23E−04 −1.45E−04 2.18E−05 2.27E−0817 0 −1.02E−01 1.52E−02 4.09E−03 −1.55E−03 1.44E−04 18 0 −1.44E−014.79E−02 −1.16E−02 1.54E−03 −8.97E−05

TABLE 6 1st 2nd Position Position D1 1.6378 0.2 D2 1.6826 0.9104 D3 0.83

The optical imaging system in the examples may have the followingcharacteristics in common. For example, a focal length of the first lensmay be within a range of 20 mm to 40 mm, a focal length of the secondlens may be within a range of −10 mm to −6.0 mm, a focal length of thethird lens may be within a range of within a range of 2 mm to 4 mm, afocal length of the fourth lens may be within a range of −15 mm to −8.0mm, a focal length of the fifth lens may be within a range of 8 mm to 15mm, a focal length of the sixth lens may be 30 mm or greater, and afocal length of the seventh lens may be within a range of −10 mm to −4.0mm. As another example, a focal length of the optical imaging system ata wide-angle end may be within a range of 5.0 mm to 7.0 mm, and a focallength of the optical imaging system at a telephoto end may be within arange of 8.0 mm to 10.0 mm.

At a wide-angle end of the optical imaging system, a distance D1 betweenthe first lens group and the second lens group may be greater than adistance D3 between the third lens group and the imaging plane, and adistance D2 between the second lens group and the third lens group maybe greater than the distance D3 between the third lens group and theimaging plane. At a wide-angle end of the optical imaging system, D1/D2may be within a range of 0.9 to 1.3, D2/D3 may be within a range of 1.5to 2.2, and D1/D3 may be within a range of 1.5 to 3.5.

At a telephoto end of the optical imaging system, the distance D1between the first lens group and the second lens group may be smallerthan the distance D2 between the second lens group and the third lensgroup, and the distance D2 between the second lens group and the thirdlens group may be smaller than the distance D3 between the third lensgroup and the imaging plane. At a telephoto end of the optical imagingsystem, D1/D2 may be within a range of 0.2 to 0.4, D2/D3 may be within arange of 0.2 to 0.4, and D3/D1 may be within a range of 14 to 16.

Table 7 lists values of the conditional expressions of the opticalimaging system of the first and second examples. As indicated in Table7, the optical imaging system may satisfy all of the aforementionedconditional expressions.

TABLE 7 Conditional 1st 2nd Expression Example Example R2/f −0.91365−0.92417 (R1 + R2)/(R1 − R2) −0.38473 −0.39535 f/f1 0.26808 0.21104 f/f31.85759 1.82593 f/f4 −0.62552 −0.63025 f/f5 0.56269 0.51286 N6-N70.11590 0.12890

According to the examples, a curved optical imaging system capable ofvarying a focal length and having a reduced size may be implemented. Theexamples provide an optical imaging system having a variablemagnification function while having a reduced size.

While this disclosure includes specific examples, it will be apparentafter an understanding of the disclosure of this application thatvarious changes in form and details may be made in these exampleswithout departing from the spirit and scope of the claims and theirequivalents. The examples described herein are to be considered in adescriptive sense only, and not for purposes of limitation. Descriptionsof features or aspects in each example are to be considered as beingapplicable to similar features or aspects in other examples. Suitableresults may be achieved if the described techniques are performed in adifferent order, and/or if components in a described system,architecture, device, or circuit are combined in a different manner,and/or replaced or supplemented by other components or theirequivalents. Therefore, the scope of the disclosure is defined not bythe detailed description, but by the claims and their equivalents, andall variations within the scope of the claims and their equivalents areto be construed as being included in the disclosure.

What is claimed is:
 1. A optical imaging system, comprising: a firstlens group configured to move in an optical direction and havingnegative refractive power; a second lens group configured to move in theoptical direction and having positive refractive power; and a third lensgroup configured to move in the optical direction and having negativerefractive power, wherein the first lens group, the second lens group,and the third lens group comprise seven lenses in total, and wherein atleast one of the seven lenses includes an aspherical surface.
 2. Theoptical imaging system of claim 1, wherein at least one of the sevenlenses is made of a plastic material.
 3. The optical imaging system ofclaim 1, wherein the first lens group comprises two lenses havingrefractive power with different signs.
 4. The optical imaging system ofclaim 1, wherein the second lens group comprises three lenses, whereinthe three lenses of the second lens group are disposed such that thethree lenses have refractive power having signs different from signs ofrefractive power of adjacent lenses in the second lens group.
 5. Theoptical imaging system of claim 1, wherein the third lens groupcomprises two lenses having refractive power with different signs. 6.The optical imaging system of claim 1, further comprising: a refractiveprism disposed in front of the first lens group.
 7. An optical imagingsystem, comprising: a prism; a first lens having positive refractivepower; a second lens having negative refractive power; a third lenshaving positive refractive power; a fourth lens having negativerefractive power; a fifth lens having positive refractive power; a sixthlens having positive refractive power; and a seventh lens havingnegative refractive power, wherein the prism and the first to seventhlenses are sequentially disposed from an object side.
 8. The opticalimaging system of claim 7, wherein the first lens comprises a conveximage-side surface.
 9. The optical imaging system of claim 7, whereinthe second lens comprises a convex object-side surface.
 10. The opticalimaging system of claim 7, wherein the third lens comprises a conveximage-side surface.
 11. The optical imaging system of claim 7, whereinthe fourth lens comprises a concave object-side surface.
 12. The opticalimaging system of claim 7, wherein the sixth lens comprises a concaveobject-side surface.
 13. The optical imaging system of claim 7, whereinthe seventh lens comprises a concave image-side surface.
 14. The opticalimaging system of claim 7, wherein at least one of the lenses comprisean aspherical surface.
 15. The optical imaging system of claim 7,wherein:−1.0<(R1+R2)/(R1−R2)<−0.1, where R1 is a radius of curvature of anobject-side surface of the first lens, and R2 is a radius of curvatureof an image-side surface of the first lens.
 16. The optical imagingsystem of claim 7, wherein:0.11<Nd6−Nd7<0.13, where Nd6 is a refractive index of the sixth lens,and Nd7 is a refractive index of the seventh lens.
 17. The opticalimaging system of claim 1, wherein, at a wide-angle end of the opticalimaging system, a distance D1 between the first lens group and thesecond lens group is greater than a distance D3 between the third lensgroup and an imaging plane, and a distance D2 between the second lensgroup and the third lens group is greater than D3.
 18. The opticalimaging system of claim 17, wherein D1/D2 is within a range of 0.9 to1.3, D2/D3 is within a range of 1.5 to 2.2, and D1/D3 is within a rangeof 1.5 to 3.5.
 19. The optical imaging system of claim 1, wherein at atelephoto end of the optical imaging system, a distance D1 between thefirst lens group and the second lens group is smaller than a distance D2between the second lens group and the third lens group, and D2 issmaller than a distance D3 between the third lens group and an imagingplane.
 20. The optical imaging system of claim 19, wherein D1/D2 iswithin a range of 0.2 to 0.4, D2/D3 is within a range of 0.2 to 0.4, andD3/D1 is within a range of 14 to 16.